Metals such as nickel, vanadium, and iron which are present in hydrocarbon feedstocks are known to have detrimental effects on the performance of a cracking catalyst used to crack such a hydrocarbon feedstock. Efforts have been made to mitigate these detrimental effects by passivating these metals. Antimony, antimony oxide and other compounds of antimony have been proposed for this passivation. Antimony and its compounds are, however, fairly expensive chemicals and the most efficient use thereof constitutes an important economic goal.